1. Technical Field
The present invention relates to a headlamp apparatus for a vehicle such as a car and more particularly to a detecting device for detecting the straight steering direction of a vehicle in a headlamp apparatus comprising light distribution control means for changing the direction and range of irradiation of a headlamp in the steering direction of the vehicle, for example, an adaptive illuminating system (hereinafter referred to as an AFS (Adaptive Front-lighting System).
2. Background of the Related Art
The related art AFS proposed to enhance the running safety of a car detects information about the running situation of a car CAR by means of a sensor and sends a detection output to an electronic control unit (hereinafter referred to as an ECU (Electronic Control Unit)) 2 as shown in FIG. 1. For the related art sensor, there is used a steering sensor 11 for detecting the steering angle of a steering wheel 12 provided in a steering device 1 of the car CAR, for example. Based on the output of the steering sensor 11, the ECU 2 controls lamps which are provided on the left and right of the front part of the car that can swivel respectively, that is, headlamps 4L and 4R capable of deflecting and controlling an irradiating direction into a transverse direction, thereby changing a light distribution characteristic thereof.
The headlamps 4L and 4R include an actuator to be rotated by means of a driving force source such as a driving motor for a structure in which a reflector and a projector lamp provided in a lamp housing can be rotated in a horizontal direction, for example. According to the related art AFS, when the car travels on a curved road (a curved path), it is possible to illuminate a road to be a source of the curved path corresponding to the running speed of the car, which is effective for enhancing a running stability.
In such a related art AFS, initialization is carried out to turn the swivel lamp in a straight running direction when the steering wheel of the car is steered in the straight running direction. For this reason, it is necessary to detect a steering position (hereinafter referred to as a straight steering position) in the straight running direction of the steering sensor.
In the steering sensor, as shown in FIG. 8(a), a large number of unit slits 113 are formed in a circumferential direction over a rotary disk 11 to be rotated integrally with the steering wheel 12, and furthermore, an origin slit 115 for detecting an origin position is formed at the inside diameter of the unit slit 113. The unit slits 113 and the origin slit 115 are provided with slit detectors DA, DB and DZ such as photo interruptors respectively and are constituted to generate pulse signals PA, PB and PZ corresponding to the slit from the slit detectors DA, DB and DZ with the rotation of the rotary disk 111 as shown in FIG. 8(b).
More specifically, the origin slit 115 outputs the pulse signal PZ to be an origin position signal from the origin slit detector DZ in the straight steering position of the steering wheel 12, the straight steering position of the steering wheel 12 can be detected in response to the origin position signal PZ, and the pulse signals PA and PB sent from the unit slits DA and DB are counted so that the amount of rotation of the steering wheel 12, that is, the steering angle can be detected.
In an ordinary vehicle, however, the steering wheel is constituted to be rotated plural times (generally, three rotations or more). As shown in FIG. 8(b), therefore, the origin position signals PZ (ZR, ZC and ZL) are output for each rotation of the steering wheel, respectively. Thus, it is hard to detect the straight steering position from only the origin position signal PZ. As shown in FIG. 8(a), the origin slit 115 is constituted to output the pulse signal PZ over a predetermined length range in the circumferential direction in consideration of an assembly error in the steering device. For this reason, the origin position signal has a predetermined width in an angular direction (which will be referred to as an origin zone). When the straight steering position is to be determined, the zone width of the origin zone becomes an error. Thus, it is hard to detect the straight steering position with high precision.
In Japanese Patent No. 1884151 (hereafter “JP'151”), there has been proposed a technique for deciding a straight steering position based on an origin position signal to be output when the car has a predetermined vehicle speed. In Japanese Patent No. 2514834 (hereafter “JP '834”), there has been proposed a technique for dividing an origin zone into a plurality of subzones and setting, to be an origin position signal, the signal of the subzone from which the signal is to be output continuously for at least a predetermined time, thereby deciding a straight steering position.
In Journal of Technical Disclosure No. 2002-2053 issued by Japan Institute of Invention and Innovation (hereafter “JIII '053”), there has been disclosed a technique for detecting the speeds of the left, right, front and rear wheels of the car by a speed sensor without using the origin position signal sent from such a steering sensor and recognizing a straight running state when the speeds of both front wheels are equal to each other. In this technique, the steering angle is calculated at a speed ratio of the wheels including the rear wheel when the speeds of both front wheels are different from each other.
However, the foregoing related has various problems and disadvantages. In JP '151, it is hard to carry out detection until the car travels a predetermined distance and at least a predetermined speed has been reached. Therefore, there is a problem in that a significant time is required for detecting a straight steering position. In the case in which a steering angle is exactly coincident with a steering angle at which the origin position signal is to be output when the car travels on a constant curved path, there is a possibility that an angle position for the steering might be erroneously detected as a straight steering position.
In the JP '834, a complicated structure is provided for carrying out processing of dividing the origin zone into a plurality of subzones and selecting the subzone corresponding to a time. In the detection, a predetermined time is required for carrying out the processing, and furthermore, there is a possibility that a steering angle might be erroneously detected as a straight steering position when the car travels on a constant curved path in the same manner as in the case of JP '151.
In JIII '053, the decision is carried out based only on a difference in the speed between both front wheels. Also in the case in which the speeds of both front wheels are slightly different from each other, therefore, it cannot be decided that the straight running is carried out. For this reason, an erroneous detection is caused. In this case, it can be proposed that a margin is provided in a difference in the speed between both front wheels to prevent an error from being detected erroneously. When the car travels at a low speed, the difference in the speed is very small. Therefore, when the difference in the speed enters a margin range, it is hard to detect a straight steering position with high precision.
Moreover, JIII '053 has disclosed that this technique can be used together with a signal obtained from the steering sensor described in the techniques of JP '151 and JP '834. This technique is complementary, that is, the AFS is maintained in response to another signal even if either of them is broken down. When any such signal is utilized, it is hard to eliminate the drawbacks.